Regulating circuit for energizing variable resistance loads



Feb. 4, 1958 M. J. MULHERN 2,822,507

REGULATING CIRCUIT FOR ENERGIZING VARIABLE RESISTANCE LOADS Filed July18, 1952 Fig.2.

u w v if I 1 3 f l 2 I TURNS=400 g 3 1 I I FILAMENTS l 1 COLD B:

I l 1 I I RMS LOAD CURRENT Q Inventor: Marvin J-MUIhEFfi is Attornex.

REGULATING CIRCUIT FOR ENERGIZING VARIABLE RESISTANCE LOADS Marvin J.Mulhern, Schenectady, N. Y., assignor to Gem eral Electric Company, acorporation of New York This invention relates to a regulating circuitfor energizing variable resistance loads and more particularly to anarrangement for controlling the energization of a load circuit such asthe filament of an electronic tube so as to prevent damage theretoduring the warm-up period and so as to maintain substantially constantcurrent thereto during normal operation.

The resistance of the filaments of certain electronic tubes varies froma very low value at room temperature to a value substantially in excessthereof as the tube filament is heated to its normal operatingtemperature. In certain instances, the resistance at normal operatingtemperature of a tube filament may be as much as four times theresistance of the filament at room temperature. Thus, if full voltagewere directly applied to such a filament when cold, an excessive currentwould flow resulting in probable damage to the filament, or in reducedlife of the filament.

A principal object of this invention is to provide an improvedregulating circuit for energizing variable resistance loads in such away as to prevent the application of excessive currents to the load whenthe resistance thereof is at low values and for controlling the currentflow during normal operating conditions.

In accordance with the invention, a saturable reactor having a mainwinding constructed of two sections magnetically in opposition to eachother is arranged in series with'a load circuit so as to supplyalternating current thereto. The winding sections of the reactor may beconnected in series or in parallel with respect to each other providedtheir magnetic circuits are in opposition. A pair of control windingswhich are magnetically coupled with both sections of the main windingare arranged to be energized with direct current. One of these controlwindings is supplied from a controllable source of direct current ofsuch value that the current supplied through the main winding of thesaturable reactor cannot damage the load. The other control winding isarranged to be energized by direct current which is dependent upon thevolt-.

age of the load only after the load voltage has reached a predeterminedvalue such as eighty percent of its normal value.

The principle upon which the invention is based is that the average loadwinding ampere turns of the saturable reactor must be equal to theaverage control winding ampere turns so long as the saturable reactor isoperating in the proportional region.

A comprehensive discussion of the characteristics of saturable reactorscan be found in a paper presented by H. F. Storm before the AmericanInstitute of Electrical Engineers in May of 1950 and which apears atpage 756, vol. 69, part II, of the transactions of the AmericanInstitute of Electrical Engineers.

For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction'with the accompanyingdrawing, in which:

Fig. 1 is a schematic representation of a regulating arrangementembodying the invention;

nited' States Patent Fig. 2 is a pair of load voltage versus loadcurrent characteristic curves to aid in understanding the principles ofthe invention;

Fig. 3 is a schematic diagram illustrating some of the constructionalfeatures of the saturable reactor utilized in carrying out theinvention.

With reference to Fig. 1, electronic tubes 1 and 2 are providedrespectively with filament elements 3 and 4. The filaments 3 and 4 arerespectively energized by the secondary windings of transformers 5 and6. The 'primary windings of transformers 5 and 6 are energized from asecondary winding of a potential transformer 7 whose primary winding isenergized from an alternating current source through the switch member8. Arranged in series with the secondary winding of the transformer 7are the parallel-connected main windings 9 and 10 of a saturable reactorgenerally designated by the numeral 11. Saturable reactor 11 is alsoprovided with a pair of control windings 12 and 13 which are arranged sothat the magnetomotive forces thereof are in opposition to each other.The saturable'reactor 11 could be physically arranged in any knownmanner. For example, the main windings 9 and 10 could be disposed on theouter legs of a threelegged core, and the two control windings 12 and 13could be mounted on the middle leg of the three-legged core. The mainwindings 9 and 10 could be connected in series if desired, but in eithercase their magnetic circuits must be in opposition as indicated in Fig.3.

Control winding 12 is energized through an adjustable resistance 15 froma source of direct current energy indicated at 14 in the form of aconventional rectifier arrangement. The rectifier arrangement 14 isenergized from alternating current derived from the secondary winding 16of the transformer 17 having a primary winding 18. The primary winding18 of transformer 17 is energized from a secondary winding of a stepdowntransformer 19 whose primary winding is arranged to be energized fromthe alternating current source through the switch 8. Capacitor 20 and aportion of the secondary winding 16 of transformer 17 comprise a voltagestabilizing means which maintains constant voltage output irrespectiveof variations in the voltage of the alternating current source.

Thus, it will be understood that by suitable adjustment of the variableresistor 15, a desired magnitude of direct current is supplied to thewinding 12 so that a predetermined magnitude of current is supplied tothe filaments 3 and 4 through the transformers 5 and 6, the saturablereactor 11 being essentially a constant current device which supplies aconstant magnitude of current substantially independent of theresistance of the load and determined by the magnitude of the directcurrent supplied to winding 12. As the filaments 3 and 4 warm up, theirresistance increases and the voltage thereacross increases since thecurrent is maintained at a substantially constant value.

In accordance with one feature of the invention, control winding 13 isenergized in accordance with the load voltage, and at such time as theresistance of the filaments 3 and 4 reaches a value such as eightypercent of its normal operating value, winding 13 begins to effectcontrol of reactor 11. To this end, a transformer 21 having a primarywinding 22 and a secondary winding 23 is connected in parallel with theprimary windings of the 'transformers 5 and.6, and a rectifierarrangement 24 is arranged to be energized from a secondary winding 23.

Connected across the direct current output terminals of the rectifier 24is a smoothing capacitor 25 and a bias resistor 26. The voltage acrossthe bias resistor 26 is I unidirectional conducting device 28 and theresistor 29. From the circuit described thus far, it will be understoodthat the various elements could be selected and adjusted so that nocurrent would flow through the winding 13 until after the voltage of theload and, hence,'the voltage of the secondary winding 23 of thetransformer 21 reaches a predetermined value. At such time as thevoltage of the load increases to a predetermined value, a current thenbegins to flow through the control winding 13, the rectifier 28 beingeffective to prevent reverse fiow of current through winding 13 when theload voltage is below the above-mentioned predetermined value. b

In accordance with a feature of the invention, the magnetomotive forceof the winding 13 is arranged so as to oppose the magnetomotive force ofthe winding 12. Thus, during the initial portion of the warm-up period,the .winding 12 and the main windings 9 and 10 act as a constant currentdevice-to supply substantially constant current to the filaments3;and-4. Thereafter, when the resistance of these filaments increases tosome amount such as to eighty percent of its normal value, then acurrent begins to flow through the control winding 13, the magnitude ofwhich increases as the magnitude of the load voltage increases. Sincethe winding 13 opposes the magnetizing action of the winding 12, theeifect of the winding 13 is to tend to reduce the voltage across theload and also the current thereto.

The particular operation of the circuit described above will be morefully understood from Fig. 2. In Fig. 2, two curves are plotted of loadvoltage against load current, one .curve being for control ampere turnsof 509 such as might be efiective with only winding 12 energized,

i. e., with control winding 13 deenergized, and the other.

being'for control ampere turns of 400 such as might be the effective-netampere turns when both opposed control windings are energized. Thus,from Fig. 2, it will be understood that approximately 159 percent loadcurrent could ,be drawn with the filaments cold and with control ampereturns of 500. As the load is warmed up, 100 percent load is achievedwith the filaments hot due to the reduction in net ampere turns due tothe opposing effect of winding 13 and winding I12.

From the above description, it will be understood that by the inventionthe magnitude of current is limited initially due to the saturablereactor 11 acting as an essentially constant current device andthereafter the loadcurrent is reduced due to the regulating effect ofthedwinding 13'which is responsive to the voltage of the loa ,Inordertop'revent an excess current from being supplied to the filaments 3and t at the instant the switch 8" is closed, a relay 30 is, providedhaving its normally closed contacts 31 connected across the primarywindings of the transformers 5, 6 and 21. Thus, it is impossible tosupply an excess current to the filaments 3 and '4 so long as the shortcircuit maintained. Shortly after the switch 8 is closed and at suchtime as the high inrush current will have diminished to a safe value,the timedelay relay 32 closes its contacts 33 so as to energize the coilof relay 3t) thereby to cause the contacts 31 to be opened'and'the shortcircuit removed from across the primary windings of the transformers 5,6 and 21.

'While' I have described and shown a particular embodiment of theinvention, I'do not wish to be limited;

theretoand intend in the appended claims to cover all such changes andmodifications asfall within the true spint and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a source of alternating current, a load connectedthereto, a saturable reactor having a main winding constructed of twomagnetically opposed sections, said winding being in series with saidload, a pair of control windings magnetically coupled with both of saidsections of said main winding, an energizing circuit independent of saidload for supplying controllable direct current to one of said controlwindings so as to maintain the current to the load at a predeterminedvalue, and circuit means coupled to said-load and responsive to the loadvoltage for supplying direct current to the other of saidcontrol'windings for values of load voltage in excess of a predeterminedvalue.

2. In combination, a source of alternating current, a load connectedthereto, a saturable reactor having a main winding constructed of. twomagnetically opposed sections, said winding being in series with saidload, a pair of control windings magnetically coupled with both of saidsections of said main winding, an energizing circuit coupled to saidsource and independent of said load for supplying controllable directcurrent to one of said control windings, and circuit means coupled tosaid load and responsive to a quantity which is representative of theload voltage for supplying direct current to the other of said controlwindings, the magnetomotive force of said control windings being inopposition and the resistance of the load being, substantially greaterwhen at normal operating temperature than when at ambient temperature,and means in said circuit means to prevent the flow of current to saidother control winding when the load voltage is ;below a predeterminedvalue.

3. An arrangement for regulating the supply of current to the filamentof an electronic tube, comprising a source of alternating current,a-load including a filament of an electronic tube connected thereto, asaturable reactor hav- :ment for energizing one of said controlwindings, so as to tend to maintain a substantially constant current tosaid filament irrespective of'the resistance thereof, a source of directreference voltage, means in circuit with said alternating current-sourceandsaid load for deriving a voltage proportional to the load voltage,and uni-directional conducting means for connecting the other of saidcontrol windings between said-source of direct reference voltage andsaid voltage derivation means, said uni-directional conductingmeansbeing poled in a direction to enable the flow of current-through saidother control winding only when said derived voltage exceeds said directreference voltage.

4. The arrangement as defined in claim 3 further com prising meansnormally short circuiting said load and said voltage deriving means toprevent supply of overcurrent thereto, and time-delay means fordisabling said shortcircuiting means when the resistance of saidfilament has attained a predetermined value.

Referenccs Cited in the file of this patent UNITED STATES PATENTS2,278,151 Runaldue Mar. 31, 1942 2,331,411 Mila'rta ,Oct. 12, 19432,549,782 Engleman Apr. 24, 1951

